A hybrid electric vehicle (HEV) includes two power sources for delivering power to propel the vehicle. Typically, the first power source is an engine which consumes fuel to deliver power and the second power source is a battery which stores and uses electric energy stored to deliver power.
A plug-in hybrid electric vehicle (PHEV) is an extension of HEV technology. The PHEV battery has a larger capacity and is rechargeable from an external electric grid.
A HEV and a PHEV buffer fuel energy and recover kinematic energy in electric form to improve the fuel efficiency. For a HEV, fuel for the engine is the principal energy source. A PHEV has an additional principal energy source—the electric energy stored in the battery from the grid after a charging event.
A HEV is typically operated to maintain a state of charge (SOC) of the battery near a constant charge level. In contrast, a PHEV is expected to use as much electric energy as possible before the next charging event; i.e. the relatively low-cost grid supplied electric energy is expected to be fully used after a charging event.
To this end, two basic operating modes for a PHEV include a charge depleting (CD) mode and a charge sustaining (CS) mode. During a first travel distance after a charging event, the fully/partially charged PHEV is driven in the CD mode, where primarily the electric energy is used to propel the vehicle, gradually depleting the battery SOC. In particular, a vehicle system controller or the like decides the power sourcing proportioning between the fuel and the electric energy to meet the propulsion requirements of the driver with the use of the electric energy being prioritized. Once the battery SOC decreases to a predefined charge sustaining SOC level, the PHEV is driven in the CS mode. In the CS mode, the battery SOC is kept near the charge sustaining level and the vehicle is mainly powered by the engine (i.e., fuel energy) as is done in typical HEV operation.
The fuel economy of a PHEV can be optimized if the battery usage is adapted for the exact distance that the vehicle will be driven until the next charging event. In particular, the fuel economy of a PHEV can be optimized if the CD mode operation is extended to the exact distance that the vehicle will be driven until the next charging event.